This invention relates generally to a method and means for preventing freezing of the coupling valves during transfer of a cryogenic liquid from one vessel to another.
More specifically, this invention relates to means for preventing freezing of the quick disconnect coupling during charging of a portable liquid oxygen container from a stationary storage container in home oxygen therapy systems.
A number of commercially available systems have been developed to provide supplementary oxygen for persons of impaired breathing ability. Such systems typically comprise a relatively large capacity stationary container and a small portable container having a capacity sufficient to provide several hours use. The large stationary container typically is sized to hold sufficient liquid oxygen to provide one to two weeks of continuous oxygen therapy. It is used as the oxygen supply for in-home use and as a refill source for portable units.
Size and weight considerations govern the capacity of portable liquid oxygen therapy units. Such units usually are sized to provide about three to about fourteen hours of continuous oxygen supply; adequate for a person working normal hours and for shopping, visiting and other short trips. In preparation for use, the portable unit is filled with liquid oxygen from the stationary home unit. The stationary and portable units are equipped with mating, quick-connect couplings to allow refill of the portable unit and to allow periodic recharging of the home unit.
The quick-connect coupling comprises a male fitting, preferably associated with the portable unit, and a female fitting, preferably associated with the stationary unit. Both male and female fittings include a normally closed poppet valve which valves are locked into an open position when coupled in a mating posture. Filling of the portable unit is then accomplished by venting gas from the portable unit allowing liquid oxygen, under positive pressure in the stationary container, to flow through the coupling and fill the portable unit. The two units are then disconnected causing the spring loaded poppet valves in both male and female fittings to automatically close.
Liquid oxygen is extremely cold having a normal boiling point of about -297.degree. F. Flow of liquid oxygen through the fill tubulation and quick-connect coupling condenses and freezes moisture from the air on the coupling and tubulation. This effect is most extreme in a humid environment and often results in an ice build-up on the coupling sufficiently thick and strong as to render uncoupling impossible.
The ice-locked coupling can be freed simply by leaving the two containers in a coupled position long enough for the ice to melt; typically some five to fifteen minutes. However, many users of liquid oxygen therapy systems do not sufficiently understand the cause and cure of this icing problem to cope with it. They often will attempt to force disengagement of the coupling, risking damage to one or the other of the units, or will consider the units to be broken requiring an unnecessary service call.
Besides causing inconvenience to the user, icing an cause damage to the quick-connect coupling itself. The female portion of the coupling is fitted with a resilient seal forming a press fit with the male portion to prevent leakage of liquid oxygen during filling. Ice in the coupling causes abrasive damage to the sealing gasket during the uncoupling procedure. This gasket damage then allows linkage of liquid oxygen during subsequent refilling operations.
The problems associated with condensation and freezing of moisture on couplings during the transfer of cryogenic fluids in general, and of liquid oxygen in particular, have long been recognized. Yet the art has failed to provide any effective means to avoid the icing of couplings of sufficiently uncomplicated nature as to allow its use on oxygen therapy systems.